The present invention relates generally to an omnidirctional rolling support. More particularly, this invention concerns a caster for supporting moveable objects.
Throughout the better part of a century, people have been using casters positioned on the bottom of heavy objects to facilitate moving those objects from one place to another. Generally, the casters are intended to permit the object to be rolled in any direction that may be desired so that effort need not be expended to lift the object. The ability to permit movement in a large number of different directions is typically accomplished by mounting a wheel for rotation on a horizontal axis and then mounting that horizontal axis axis of rotation so that it is horizontally displaced from a vertical axis by means of which the device is attached to the heavy object. When the object is pushed in a horizontal direction, the horizontal offset establishes a force couple that causes the wheel to trail the object in its direction of movement in response to the force resulting from the horizontal push. This alignment of the wheel in a position following the direction of travel is a castering action.
In order to improve the castering function of such devices, a bearing assembly is sometimes provided which reduces the frictional resistance to movement about a vertical axis. When a ball bearing is used in this environment, the horizontal offset of the axis of the wheel from the vertical axis of the bearing imposes a force moment on the ball bearing which places one or perhaps two of the bearing balls under a force loading which corresponds to the entire weight of the object being supported. Imposition of this force loading on the one or two bearing balls, rather than distributing the force load on all of the bearing balls, leads to premature wearing out of the ball bearing assembly, and sometimes to premature failure of individual bearing balls. As a result, the imbalance or lack of symmetry in the force loading is seen to be a problem leading to reliability and failure concerns.
Another problem with known caster assemblies is their use of relatively small diameter wheels. Small diameter wheels essentially increase the local bearing pressure on the underlying surface. Such increased bearing pressure causes marring of wood floors and resilient flooring materials such as vinyl and the like. And, where the caster assembly is used to support an object on a floor which is covered with a high or medium height pile, the small diameter of the wheel contributes to a substantial increase in the effort needed to move the object.
Moreover, it has been observed that probably the most common use which caster assemblies are required to provide is the ability to reverse direction of movement. This is the movement which is required for example when a homeowner pulls a refrigerator out of its normal position in a kitchen for cleaning purposes and then returns the refrigerator to that normal position. Similarly, when a desk chair is rolled under a desk, the most common movement is a reversal of direction to permit the chair and its occupant to move backwardly and away from the desk. Where the caster assembly is required to undergo a direction reversal, the horizontally offset wheel must pivot about the vertical axis through a direction of 180 degrees. When four or more independent wheels experience that angular change, erratic movement of the object from side to side frequently occurs. As a result, it is difficult to position and withdraw an object on caster from spaces which do not provide adequate lateral clearance.
Another problem which is sometimes encountered when using known caster assemblies concerns the presence of imperfections in the horizontal surface supporting the caster assembly. Slight inclinations and slight vertical offsets in the underlying surface can, and often do, cause damage to the edge of the caster wheel. Such damage can lead to sharp broken edges that can seriously damage the underlying surface.
One known caster assembly includes a wheel contained in a cage so as to be moveable between two positions, each of which is horizontally offset from the vertical axis of support. In moving between these two positions during reversal of direction, the vertical load being supported is transferred to the periphery of the wheel. See, U.S. Pat. No. 1,839,396, issued to Kimball on Jan. 5, 1932. A similar device is known in which a pair of wheels are mounted on an axle which in turn is moveable between two positions. Movement of the axle permits the caster device to move and reverse directions on a straight line. Vertical forces are supported by a pair of bearing wheels, only one of which for the reasons discussed supports the vertical load. See, U.S. Pat. No. 343,725, issued to Pederson on June 15, 1886. Such devices, however, apply the unbalanced force moments to the bearing elements so that those elements are subjected to unusually rapid wear and failure.
A caster assembly is also known in which the wheel is mounted by a spherical bearing in such a manner that the yoke carrying the wheel or wheels is inclined relative to the vertical direction in a vertical plane perpendicular to the horizontal axis of the wheel. That inclination provides the horizontal offset which generates the castering action. And, the horizontal axis of the wheel is also permitted some freedom to tilt in the vertical direction. See, U.S. Pat. No. 2,560,562 issued to Ferwerda on July 17, 1951. The ability of a caster assembly to accomodate movement of its horozontal axis in a vertical plane is also known in more conventional devices in which the vertical axis is horizontally displaced from the axis of the wheel. See, U.S. Pat. No. 1,622,447 issued to Kalberer on Mar. 29, 1927.
It is also known to use a tire in connection with a caster assembly where the horizontal axis about which the wheel rotates is displaced horizontally from the vertical axis about which the caster is free to move. See, U.S. Pat. No. 696,499 issued to Schaibly on Apr. 1, 1902.